The invention relates to a corrugator for ribbing plastic pipes comprising two synchronously circulating chains of mold halves, guide means for the mold halves having an input zone in which the associated mold halves are brought into engagement with each other, a molding zone in which a central channel is provided for guiding the engaged mold jaws and an output zone in which the mold halves are again separated from each other, as well as return guides for the mold halves on the path between the output and input zones and cooling means for cooling at least the central channel with a coolant.
In such a conventional corrugator usually the molding zone with the central channel is separated from the return guides arranged on the two longitudinal sides thereof. In the running direction of the central channel in the two side walls thereof meander-like coolant passages are provided and the sealing outwardly is by suitable sealing means and an outwardly arranged plate at each of the two longitudinal sides. The cooling passages are relatively complicated and therefore expensive to make; this is also enhanced by the necessary seals. Furthermore, the setting up of such a corrugator involves a relatively great amount of work. This is essentially due to the fact that the central channel and each of the two return guides must be separately aligned.
If the return guides are to be cooled as well, meander-like coolant passages are also to be provided in the corresponding walls of the return guides and just like the central channel said passages must be sealed via suitable sealing means and an outer plate. This makes the conventional corrugator still more complicated to manufacture and difficult to handle.
The central channel in known corrugators is subject to a relatively high wear because the running surface for the mold halves which are pressed against each other in the central channel are subjected to the forces arising in the forming of the ribbing (caused by the excess pressure in the interior of the plastic pipe).
Furthermore, the known corrugator arrangement is not very flexible from the point of view that, by the fixed cross-section and the fixed form of the coolant passages, it is difficult to vary the cooling power within a larger range. This is a disadvantage in particular when a change of the particular plastic used is carried out frequently.
Furthermore, a corrugator has already been proposed which has a very complicatedly formed lower portion and a cover placed thereon for sealing. In the lower part in the center of the central channel, in each case separated on the outside on both sides by a wall, in substantially U-shaped manner a cavity is provided having in each case a spray cooling means for the central passage, and on the outside the two return guides are provided, once again separated via a wall. These five adjacently disposed upwardly open spaces are sealed by the common cover with suitable sealing means so that the spaces are upwardly closed. Admittedly, due to the spray cooling for the central channel the hitherto necessary coolant passages are dispensed with; however, said lower part can be made only at very high cost. The numerous sealing points between the cover and the lower part lead to having to adopt very complicated steps for the sealing or to an impairment of the operational reliability.
On occurrence of the relatively high wear of the central channel as described above the entire lower part and the cover must be replaced because both these parts form the central channel.